It's been a while since I checked my terms as a dev, but I think that it's 70/30 In favour of the Dev (i.e. 70c per Dollar).
Why charge on one platform not another? Well... the Android Platform is notorious for pirated apps, so why bother, and on the iTunes App Store, whatever your app is, there will be many more free versions doing the same thing maybe better. On BbApp world, you can charge, and I'd say that's why many people do.
Just a thought or two!
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